1. Field of the Invention
The invention relates to a method for the cutting or shaping machining of metallic or ceramic workpieces using a preferably submerged tool, in which, during the machining operation, a coolant which at least predominantly comprises carbon dioxide (CO2) is fed to the machining location.
The invention also relates to a tool for carrying out the method described above.
2. Background Description
The method described in the introduction can be found in DE 43 26 517 C2. This document discloses a method for the cutting machining of metallic workpieces and also ceramic surfaces, in which, as a result of a coolant being fed to the machining location, cooling is carried out during the machining operation, and in which, for cooling purposes, a coolant jet which predominantly comprises carbon dioxide and includes cold gas and snow particles, is fed to the machining location. The coolant jet is obtained from gaseous CO2 which is under a suitable superatmospheric pressure, in such a manner that the CO2 gas, via a slot nozzle or other slot-like opening, is first of all expanded into an expansion volume which is formed around this expansion slot and is substantially closed off from the environment, and the cooling jet is formed starting from this expansion volume and its outlet opening and is directed onto the region which is to be cooled. In this case, the starting pressure level for the CO2 prior to the expansion is at least 50 bar.
DE-B 15 509 Ib/49a has disclosed a method for the cutting machining of metallic workpieces, in which, as a result of a coolant being fed to the machining location cooling is carried out during the machining operation. The coolant used is a liquid jet of CO2 directed onto the workpiece via a nozzle. The liquid jet of CO2 strikes the workpiece at the machining location, forming a deposit of solid CO2. The liquid CO2 is intended to expand at the location where the tool touches the workpiece.
DE-AS 1 037 808 has disclosed chip-forming machining using carbonic acid in the form of snow for cooling purposes. In this case, pressurized liquid carbonic acid flows out of a capillary tube or a nozzle and as it emerges, as a result of the pressure drop, is instantaneously converted into a mixture of vapor and snow.
The cooling method based on carbon dioxide is a dry cooling method. Since at normal ambient temperature carbon dioxide adopts a gaseous state, no coolant residues remain behind on the workpiece following the cooled machining.
DE 199 15 619 A1 has described a method for discharging machining products of a machining process, in which solid CO2 particles are fed to a gas stream. The gas stream together with the solid CO2 particles which it has collected is then fed to a machining space, where it is directed onto a region in which a workpiece is being machined by a tool, taking in at least the majority of the machining products which are generated.
The article “Kühlschmieren beim Zerspanen” [Cooling and lubrication during machining] by Kurt Häuser (Technische Rundschau No. 25, Jun. 19, 1970, pages 21 and 23; Technische Rundschau No. 26, Jun. 26, 1970, pages 29 and 31) teaches the person skilled in the art to use CO2 as cooling lubricant which is to be sprayed onto the working location as a liquid jet at a high pressure (50-70 atmosphere above atmospheric pressure), where the expansion to form a gaseous coolant takes place, so that the cooling lubricant precipitates as snow at the working location.
U.S. Pat. No. 3,971,114 refers in general terms to cryogenic coolants, in particular Freon-12 as an example of an expandable gas coolant. In this case, the coolant, which is passed through a tool, is to emerge from the tool at a small opening or bore, the intention being for this bore to control the quantity of coolant; the bore is located at a distance from the actual machining location which is such that chips cannot have any adverse effect on the emerging stream of coolant.